Wave length modulation



G. L. USSELMAN 2,437,923

WAVE LENGTH MODULATION Filed Feb. 18, 1944 2 Sheets-Sheet l H g u (g/ i 2 I E 3 1L 0 .7 N) ,1 3 l i \o I 1;. IO

g '3 m Z 3 1 ml 9 o INVENTOR. t GEORGE L. USSELMAN.

BY #4 4m ATTORNEY March 3M8! G. L. USSELMAN 2,437,923

WAVE LENGTH MODULATION Filed Feb. 18, 3.944 2 Sheets-Sheet 2 SIGNAL SOURCE INVENTOR. GEORGE L. USSELMA N.

ATTORN EY Patented Mar. 16, W48

NH l STATES WAVE LENGTH MODULATION George L. Usselman, Port Jefierson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 18, 1944, Serial No. 522,878

This application concerns an improved circuit arrangement for the generation, mean frequency stabilization and timing modulation of oscillatory energy. Many frequency modulated stabilized oscillator circuits of the prior art are of the single ended circuit type. By this is meant that the oscillator comprises a single tube generator. In these arrangements the range through which the frequency or phase of the oscillations generated can be modulated is limited by virtue of the factthat a single tube oscillator is used.

The general object of the present invention is to increase the range of frequency or phase modulation of oscillatory energy without entailing distortion such as, for example, amplitude modu lation thereof.

In attaining the genera] object described above, I provide an improved system wherein a pushpull electron coupled crystal stabilized oscillation generator of the type illustrated in my U. S. Patent #2,210,015, dated August 6, 1940, is used as a generator, and wherein improved control means therefor is provided for controlling the timing of the oscillation generated in accordance with signals.

In describin my invention in detail reference will be made to the attached drawings wherein Figs. 1 and 2 each illustrate an embodiment of my improved timing modulation system. In these figures the generators are substantially similar. The improved control means including the tubes V4 and V3 are in general similar but difier from each other in details, as will appear hereinafter.

In Fig. 1, the oscillator comprises two tubes VI and V2 having their output anodes Ill and I8 coupled by impedances l2 and I2 from which the timing modulated generated oscillatory energy may be derived for utilization as desired. The anode electrodes are coupled substantially only by the electron stream to the generating electrodes. Direct current to the anode electrodes is supplied from the source B2 through resistances l2 and l 2'. The same source supplies direct current potentials to the oscillator screening grids l4 and I l through resistance It shunted by a bypass condenser. The anode like electrodes, here in the form of grids l8 and it are also connected to this source B2 by resistances 2B and 2B. These anode grids l8 and I8 operate at high radio frequency potential of the generated frequency and are connected respectively to the electrodes 4 and 2 of the crystal X. The controlling grids Z l and 24' are connected to the electrodes 3 and l of the crystal X and also operate 7 Claims. (Cl. 179-1715) 2 at radio frequency potentials. Bias for these grids are supplied by resistances 26 and 26,

The oscillation generator operates as described more in detail in my patent referred to above, and as briefly described, hereinafter. Crystal oscillations at electrodes 3 and excite the control grids 24 and 24 in differential or opposed phase relation. These oscillations in the crystal are of the well known thickness vibrations, e. g., of a frequency determined primarily by the thickness of the crystal. The excitation voltages of grids 24 and 24' are amplified in the tubes and fed from the anode like grid electrodes l8 and 18' back to the electrodes 4 and 2 respectively. These oscillations as fed back are differential or opposed in phase. The oscillations on the anode like electrode and control grid in each tube are also opposed in phase so that each tube operates to generate oscillatory energy and the oscillatory energy generated by the two tubes is so phased that the tubes act with respect to the output circuit as a single generator. The phase reversal between the control electrode 24 and anode grid l8 occurs in the crystal as well as in the tube. Assume the anode like grid electrode I8 is positive and the anode like grid electrode l8 negative and that the current is flowing through the crystal X from electrode 4 to 2. Then it is known that the current flowing in the crystal X between electrodes 3 and I will be in the same direction, that is, a fixed or generated current. Consequently, the voltage on the electrodes 3 and I is a counter voltage which is the reverse of the voltage on the electrodes 4 and 2, therefore the voltage of control grids 24 and 24' are in phase opposition to the voltages on the anode-like grid electrodes I8 and I8 which is the ideal condition for sustained oscillations.

The modulator tubes V4 and V3 have their anodes 30 and 30' coupled by coupling and direct current blocking condensers 32 and 32' to the anode-like electrodes l8 and I8 and the crystal electrodes 4 and 2 respectively.

The anode electrodes 30 and 30 derive directcurrent potential from the source Bl which may be a source common with B2, that is, a single source or separate sources. trodes 36 and 36 are coupled by phase shifting networks to the resistances l2 and I 2' respectively. These couplings are adjustable by virtue of the movable points on the resistances. The

phase shifting network in the coupling to grid 36 comprises series condensers C3 and C4 and shunting inductances L3 and L4, the purpose of the arrangement being to relatively advance the The controlling elecphase of excitation of grid 36 by the potentials derived from the output of tube V2, The phase shifting network for the grid 36' comprises series inductances LI and L2 and shunt capacity Cl and C2, the arrangement being such as to relatively retard the phase of excitation of the grid 36' by potentials from the output of tube VI. The grids 36 and36 are biased by resistances R2 and RI. These resistances and the tube input impedance are considered in arranging the phase shifting stages. The control grids are also coupled by a transformer T differentially to a signal source A. Source 49 supplies the bias for these grids. The condensers 4| are blocking and radio frequency bypassing condensers. These condensers are large but not large enough to modify, except as desired, the modulating potentials from T. The condensers 43 are coupling condensers for voltages of the generated frequency, These condensers are large and take no part in the phase shifting functions. They are D. C. blocking and R. F. bypass condensers.

The operation of the controlling means for the oscillation generator will now be described; The generator includes tubes VI and V2. The controlling or modulating circuit includes tubes V3 and V4; Radio frequency oscillations or voltages of the generated frequency are taken from the anode resistor l2 of oscillation generator'tube VI and fed back through this retarding filter network C2 L2, CI'LI and resistor R1 to the control grid of modulator tube V3. This filter is arranged in stages to give a substantially 90 phase lagging or retarding phase shift to the excitation voltage passed through l2' to the control rid 36'.

The excitation voltage taken from the anode resistor [2 of the oscillator tube V2 is passed through a phase advancing filter network C4 L4; C3 L3 and resistor R2 to the grid 36 of modulator tube V4. As indicated, this filter is arranged to provide the relative leading or advancing phase shift to the'excitation voltage supplied to the grid 36.

As brought out hereinbefore, the anodes of tubes VI and V2 oscillate 180 out of phase, so that the potentials supplied from resistances l2 and I2 to the control grids 36' and 36 of modulator tubes V3 and V4 would be 180 out of phase; except for the phase shift imparted by the phase shifting networks. The grids 36' and 36 are accordingly excited in phase with'each other but 90 out of phase with respect to the voltages on the anodes of tubes VI and V2.

The anodes 30' and 360i tubes V3 and V4 are coupled directly to the anode likegridelec trodes I8 and l8*of tubes VI and. V2 and also directly to the crystal electrodes 2 and 4. The control grids of the-modulator tubes V3 and V4 are differentially modulatedby control or sig-- nal currents. As long as tubes V3 and V4 are not modulated they deliver R. F. potentials of like phase to the crystal electrodesand oscillator tube grids and oscillator tube anode like grid electrodes. Since the connections are on opposite sides'of the oscillator circuit the effects cancel and .are substantially zero. Also since the phase relation of the modulator amplified R. F. energy is shifted 90 with respect to the phase of'the oscillator energy on the electrodes 2 and 4 the effect is again zero. This condition is maintained as long as. the modulator output is balanced, as is the case with no signal.

However, if signal is applied, these opposing modulating potentials are now unbalanced. and

the unbalanced vector is in phase relation with respect to the voltage fed back to the crystal by the oscillator tubes VI and V2, so that if modulator tube V3 is delivering more R. F. power the frequency will be deviated to the lower part of the frequency spectrum and vice versa. If modulator tube W3 is influenced by the signal to deliver more R. F. power than tube V3 then the oscillator circuit will function to deviate the oscillating frequency toward the higher frequency part of the spectrum. The frequency of these deviations will be in accordance with the signal and the amount or degree of frequency deviation will be proportional to the signal amplitude. The tubes V3 and V4 can be considered as reactance tubes, which is one way of looking at it. They can be considered also as amplifiers for the purpose of changing the amount of out of-phase R. F. power added to the crystal excitation potentials in such a way as to change the oscillator frequency, as can be seen by the vector relations.

The embodiment of Fig. 2 is in general similar to the embodiment in Fig. 1. Corresponding reference characters have been used in both figures in so far as possible, and the description of Fig. 1 applies to Fig. 2, except as noted hereinafter.

In Fig. 1 separate phase shifters are used for feeding the excitation voltages from resistances l2 and [2' to the controlling electrodes 36 and 36' of the tubes V4 and V3.

In Fig. 2 a single phase shifting network supplies excitation voltage from one of the resistors 12 or l2 to both control electrodes 36 and 36', so that they are excited in phase. This phase shifting network comprises several stages including condensers C5, C5 and C1 and resistances R5, R6 and R7. The resistor R5 also serves as a bias potential supply resistor for the control grids 36 and 36. The phase shifting network relatively advances the phase of the excitation voltage with respect to the phase of the voltage on the. anode of tube V2. Moreover, in Fig. 2, the controlling currents or signal currents are applied difierentially to the screening electrodes 46 and 46 instead of to the controlling electrodes, as in Fig. 1.

In Fig. 1 the control grids 36 and 36' being excited by relatively phase advanced and rela tively phase retarded voltages from the opposite sides of the differential output circuit are excited in phase, the phase of the exciting voltage on both grids being 90 displaced with respect to the oscillations in the output of the system.

In Fig. 2 the control grids 36 and 36 are tied directly together and therefore excited in phase by voltage passed through the same phase shifting network from one side of the output of the system. The phase shifting network is arranged to produce a substantially 90 phase shift. The phase of the excitation may be either advanced or retarded about 90 in phase. In the embodiment illustrated here it is assumed that the network relatively advances the phase, that is, the grids are excited by voltage of leading phase. The operation, however, is as described in detail hereinbefore. In the absence of modulation the potentials fed to the crystal electrodes 4 and 2 from the anodes of tubes V4 and V3 compensate and have little or no elfect on the frequency of the oscillations being generated. When one tube supplies more excitation voltage than the other compensation is no longer complete and the frequency of the oscillations generated shifts in a certain direction an amount proportional to the modulation amplitude. When the other tube output increases the frequency shifts in the other direction an amount proportional to the modulation amplitude.

The network may be connected to the resistance l2 and the eflect of the modulation is reversed. Likewise, if a phase shifting network providing a relatively phase lagging excitation'voltage is used the efiect of the modulation is reversed.

In both embodiments the switches S and Si may be operated to disconnect the anodes 30 and 30' from the crystal plates 4 and 2 and oscillator grids l8 and I8, and to connect the anodes Six and 30' to the crystal electrodes l and '5 and to the control grids 2t and 26 of oscillator tubes V2 and VI. In this case cross connections are used to maintain the same phase relation obtained when the connections are as shown in full lines. As a matter of fact, all of the connections may be reversed without afiecting operation, except that the direction of frequency deviation may be reversed.

I claim:

1. In a signalling system, an arrangement for modulating an oscillator of the regenerative type having two tubes each having a plurality of electrodes including a cathode a control grid and an anode-like electrode in a circuit including a piece electric crystal having two pairs of terminals one of which pairs couples the control grids for. differential operation and the other pair of which terminals couples the anode electrodes for differential operation, a pair of modulator tubes having output electrodes coupled differentially to corresponding electrodes of said first two tubes, and having input electrodes coupled to the generating circuits and excited through said last coupling by voltages of like phase displaced in phase with respect to the generatedvoltages, and a source of modulating potentials coupled to corresponding electrodes of the modulator tubes for differentially modulating the gains of the modulator tubes.

2. In a signalling system, an arrangement for modulating an oscillator of the regenerative type having two tubes each having an anode like electrode, a cathode and a control grid in a circuit including a piezo electric crystal having two pairs of crystal terminals, one pair of terminals being between the anode-like electrodes of the tubes and the other pair of crystal terminals being between the control grids of the tubes, a pair of modulator tubes having output electrodes coupled across a pair of said crystal terminals and connected to corresponding electrodes of said oscillator tubes, and having input electrodes coupled by phase shifting means to said oscillator to be excited by voltages displaced in phase with respect to the generated voltages, and a source of modulating potentials coupled to corresponding electrodes of the modulator tubes for differentially modulating the gains of the modulator tubes.

generating circuit, said'circuit including a piezo electric crystal having two pairs of terminals, connections between the control grids of said devices and a pair of said terminals to excite the control grids in opposed phase relation, and connections between the anode-like electrodes of said devices and another pair of said crystal terminals to excite the anode-like electrodes in opposed phase relation, whereby oscillations are generated the frequency of which are controlled in part by the dimensions of said crystal, a pair of modulator tubes each having a control grid and an anode, connections between the anodes of said modulator tubes and a pair of said crystal terminals such that the generated voltages on the anodes of said tubes are of opposed phase, a radio frequency circuit coupling said regenerative circuit to the control grids of said tubes to apply thereto oscillations of radio frequency displaced in phase by with respect to the oscillations of radio frequency at the crystal electrodes to which the anodes of said modulator tubes are connected and on said anodes, and means for difierentially modulating the potentials on corresponding electrodes of said modulator tubesto frequency modulate the oscillations generated.

5. In a signalling system an oscillation generator comprising a pair of electron discharge devices each having a cathode, an anode-like electrode and a control grid, a regenerative circuit coupling the anode-like electrodes, cathodes and control grids of said devices in an oscillation generating circuit, said oscillation generating circuit including a piezo electric crystal having two pairs of terminals, connections between the control grids of said devices and a pair or said terminals to excite the control grids in opposed phase relation, and connections between the anode-like electrodes of said devices and another pair of said crystal terminals to excite the same by voltages of opposed phase relation, the anode-like electrode and grid of each device being excited in opposed relation, whereby oscillations are generated the frequency of which are controlled in part by the dimensions of said crystal, a pair of modulator tubes each having a cathode, a control grid and an anode, a coupling between the cathodesof said modulator tubes and devices, connections between the anodes of said modulator tubes and a pair of said crystal terminals to set up generated voltages of opposed phase on the anodes of said tubes, 2. phase shifting circuit coupling said regenerative circuit to the control grid of one of said modulator tubes to apply thereto oscillations of radio frequency displaced in phase by 90 with respect to the oscillations of radio frequency at the crystal electrode to which the anode of said one modulator tube is connected, a, phase shifting circuit coupling said regenerative circuit to the control grid of the other of said modulator tubes to apply thereto oscillations of radio frequency displaced in phase 90 with respect to the oscillations of radio frequency at the crystal electrode to which the anode of said other of said modulator tubes is connected, and means for differentially modulating the potentials on corresponding electrodes of said modulator tubes to frequency modulate the oscillations generated.

6. In a signalling system an oscillation generator comprising a pair of electron discharge devices each having a cathode, an anode-like electrode and a control grid, a regenerative circuit coupling the anode-like electrodes, cathodes and control grids of said devices in an oscillation generating circuit, said circuit including a 7. piezoelectric crystal having two pairs of terminals, connections between the control grids of said devices and a pair of said terminals to excite the control grids in opposed phase relation, and connections between the anode-like electrodes of said devices and another pair of said crystal termi nals to excite the same by voltages of opposed phase relation, the anode-like electrodes and grid of each device being excited in opposed relation, whereby oscillations are generated the frequency of which are controlled in part by the dimensions of said crystal, a pair of modulator tubes each having a cathode, a control grid and an anode, a coupling between the cathodes of said modulator tubes and devices, connections between the anodes of said modulator tubes and a pair of said crystal terminals to set up the generated voltages of opposed phase on the anodes of said tubes, a phase shifting circuit coupling said regenerative eircuit to the control grids of said modulator tubes to apply thereto oscillations of radio frequency displaced in phase by 90 with respect to the oscillations of radio frequency at the crystal electrodes to which the anodes of said modulator tubes are connected and on said anodes, and means for differentially modulating the potentials on corresponding electrodes of said modulator tubes to frequency modulate the oscillations generated.

7. In a signalling system an oscillation generator comprising a pair of electron discharge devices each having an anode, a cathode, an anodelike electrode and a control grid, a regenerative circuit coupling the anode-like electrodes, cathodes and control grids of said devices in an oscillation generating circuit, said oscillation generating circuit including a piezo electric crystal having two pairs of terminals, connections be tween the control grids of said devices and a pair of said terminals to excite the control grids in opposed phase relation, and connections between the anode-like electrodes of said devices and another pair of said crystal terminals to excite the same by voltages of opposed phase relation, the anode-like electrode and grid of each device being excited in opposed relation, whereby oscillations are generated the frequency of which are controlled in part by the dimensions of said crystal, an output circuit coupled to the anodes of said devices, a pair of modulator tubes each having a cathode, a control grid and an anode, a coupling between the cathodes of said modulator tubes and devices, connections between the anodes of said modulator tubes and a pair of said crystal terminals to set up generated voltages of opposed phase on the anodes of said tubes, phase shifting means coupling said output circuit to the control grids of said modulator tubes to apply to both thereof oscillations of radio frequency displaced in phase by with respect to the oscillations of radio frequency at the crystal electrode to which the anode of said modulator tubes are connected, and means for differentially modulating the potentials on corresponding electrodes of said modulator tubes to frequency modulate the oscillations generated.

GEORGE L. USSELMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 7 Number Name Date 2,111,587 Goldstine Mar. 22, 1938 2,210,015 Usselman Aug. 6, 1940 2,250,296 Crosby July 22, 1941 2,298,436 Usselman Oct. 13, 1942 

